Plans for a series of mobile flood barriers, proposed to save the city of Venice from ever more frequent flooding, are being considered by the Italian government.

They might be designed to hold back the high tides, but they have not yet been tested against the flood of criticism they are likely to raise.

Critics say the barriers will only exacerbate the problems by causing environmental damage.

St Mark's Square - lowest point, most often flooded

There could be little argument, however, about the seriousness of the problem. Even on a good day, water slowly seeps out from under the stones in St Mark's Square, the lowest point in Venice.

And things can get a lot worse. Back in 1966, when Venice was hit by the most serious floods in its history, the water rose to 1.8 metres (six feet). In recent years the flooding has been less dramatic, but more frequent.

"The assumption is that if the barriers are installed, it will solve the flooding problem. But that clearly is not the case. The barriers, if they are installed, will serve to cream off the worst of the high tides."

Opponents also argue that the barriers would damage the unique eco-system of the lagoon, which might be an important issue for Italy's Environment Minister, a prominent green. Pro-barrier groups fear he might throw out the plan, or at least try to buy some more time.

Too much water - many residents leave for good

But with 20 years of argument about the idea, a decision must finally be made, says Paolo Costa, a former public works minister.

"The time for the analysis, the discussion, the scientific investigation is over. Now politicians have to take their own responsibility and have to decide."

For the thousands of tourists, though, the high tides are part of the attraction. But crossing St Mark's Square via makeshift pathways, or changing into wellington boots in the middle of a road is not so much fun for Venetians, who are leaving the city at the rate of 50 a week.

Abandonment is now a real threat to Venice, as well as a slow death by drowning.

In 1997 the centre of the city was flooded 80 times. According to experts, in 50 years' time there could be flooding every day.